Stone, masonry and various other substrates with surface porosity are used decoratively in the indoor and exterior environment. However, such surfaces are easily stained, for instance by oils, hydraulic fluids, and oily and aqueous foodstuffs, including oils, coffee, ketchup, salad dressings, mustard, red wine, other beverages, and fruit preserves. Many of the prior art treatments, such as clear sealants based on polyurethanes or epoxies, disadvantageously alter the appearance of the substrate. Such sealants can also trap moisture within the treated substrate, promoting spalling.
U.S. Pat. No. 4,957,948, of Terry and McIntosh describes biocidal protective coatings for heat exchangers which consist of an organic water-resistant polymer with an associated mixture of mono-alkyl and bis-alkyl phosphates. The heat exchanger coatings of Terry and McIntosh contain perfluoroalkyl methacrylate copolymers and up to 10% and preferably 1-5% by weight of an alkyl phosphoric acid or its derivative. The coatings are applied to heat exchanger coils, such as coils of aluminum or copper, to provide durable biocidal adherent coatings. In a related patent, U.S. Pat. No. 4,935,232, McIntosh describes microbiocidal phosphate additives which contain at least one free hydroxyl group. McIntosh notes in U.S. Pat. No. 4,935,232 that if all the hydroxyl groups of the microbiocidal phosphate are replaced by alkyl or other organic groups, the phosphate will no longer exhibit microbiocidal activity. There is no teaching of use of their compositions for stain resistance on hard porous surfaces.
It is desirable to improve the degree of stain resistance conferred on such substrates and also not promote spalling. The present invention provides such treatment for surfaces subject to staining.